1. The problem statement, all variables and given/known data #1 Given that the angle between the vectors a and b is 2Pi/3 and |a|=3 and |b|=4 calculate: (axb)^2 [(2a+b)x(a+2b)]^2 #2 Given three unit vectors, a, b, c such that a+b+c=0 find (a dot b) + (b dot c) + (c dot a) #3 Given AB=a+2b BC=-4a-b CD= -5a-3b where a and b are any two vectors, prove that ABCD is a trapezium 2. Relevant equations Given above 3. The attempt at a solution #1 I know that axb = |a||b|sinx and axa = 0 and axb = -b x a but i do not understand how the powers or constants affect this? #2 No idea #3 A trapezium has one set of parallel sides only and i know if vectors are parallel they are a multiple of each other, however none of these seem to be multiples of each other?